Wireless data communication equipment, such as Wireless Local Area Network (WLAN) devices, are finding widespread use in personal computer applications. They have become relatively inexpensive to deploy, finding economical use even in home computer networks.
The technology supporting the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards and other similar networking standards allows stations (STAs), e.g., portable computers, to be mobile while remaining connected to a WLAN via radio or infrared communications to access points (APs) or other STAs. These standards are designed as several layers of communication protocols. A physical layer (PHY) in the STAs provides low-level transmission means by which the STAs communicate. Above the PHY is a Media Access Control layer (MAC) that provides services, such as authentication, de-authentication, privacy, association, disassociation, etc.
Typically PHY electromagnetic signals are transmitted and received at a STA by a monopole antenna. This type of antenna typically consists of a single wire or patch antenna element. The signal transmitted from a monopole antenna is omni-directional in nature. That is, the signal is sent with the same signal strength in all directions in a generally horizontal plane for a vertical oriented antenna element. Reception of a signal with a monopole antenna element is likewise omni-directional. A monopole antenna thus does not differentiate in its ability to detect a signal in one direction versus detection of the same or a different signal coming from another direction.
Monopole antennas are susceptible to effects that degrade the quality of communication between the STAs and APs, such as reflection or diffraction of radio wave signals caused by intervening objects, such as walls, desks, people, etc. These objects create multi-path, normal statistical fading, Rayleigh fading, and so forth.
Steerable directional antennas, i.e. antennas optimized for communications in a particular direction in space, may improve signal reception when used within the STAs and increase the allowable distance between STAs and APs. Such antennas are known in the prior art.
For example, U.S. Pat. No. 6,404,386 issued to Proctor, Jr., et al. on Jun. 11, 2002, entitled “Adaptive Antenna for Use in Same Frequency Networks”, incorporated by reference herein in its entirety, describes a directional subscriber antenna apparatus. The antenna provides a plurality of antenna elements, each coupled to a respective signal control component such as a switch. The antenna array creates a beamformer for signals to be transmitted from the subscriber unit, and a directional receiving array to more optimally detect and receive signals transmitted from the base station. By directionally receiving and transmitting signals, multi-path fading is greatly reduced. Various techniques for determining the proper arrangement of signal control components for each antenna element are accommodated with this design.
U.S. Pat. No. 6,396,456 issued to Chiang, et al. on May 28, 2002, entitled “Stacked Dipole Antenna for Use in Wireless Communications Systems”, is also incorporated by reference herein in its entirety. This patent describes a dipole antenna element fabricated with printed circuit board (PCB) photo-etching techniques for precise control of the printed structure to mass-produce antenna elements with repeatable features. The antenna includes a planar substrate made of dielectric material, and can be used to fabricate inexpensive steerable antenna arrays.
A detailed discussion of a directive antenna array is provided in U.S. Patent Publication No. 2002/0008672, published Jan. 24, 2002, entitled “Adaptive Antenna for Use in Wireless Communications System”, the entire teachings of which are incorporated herein by reference. Example methods for optimizing antenna direction based on received or transmitted signals by the directive antenna array are also discussed therein and incorporated herein by reference in their entirety.